﻿/* Copyright (c) 2019 Rick (rick 'at' gibbed 'dot' us)
 *
 * This software is provided 'as-is', without any express or implied
 * warranty. In no event will the authors be held liable for any damages
 * arising from the use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 * 1. The origin of this software must not be misrepresented; you must not
 *    claim that you wrote the original software. If you use this software
 *    in a product, an acknowledgment in the product documentation would
 *    be appreciated but is not required.
 *
 * 2. Altered source versions must be plainly marked as such, and must not
 *    be misrepresented as being the original software.
 *
 * 3. This notice may not be removed or altered from any source
 *    distribution.
 */

using System.Collections.Generic;

namespace Gibbed.Borderlands2.SaveEdit
{
    public class EnumerableComparer<T> : IComparer<IEnumerable<T>>
    {
        private readonly IComparer<T> _Comparer;

        public EnumerableComparer()
            : this(null)
        {
        }

        public EnumerableComparer(IComparer<T> comparer)
        {
            this._Comparer = comparer ?? Comparer<T>.Default;
        }

        public int Compare(IEnumerable<T> x, IEnumerable<T> y)
        {
            var comparer = this._Comparer;
            using (var left = x.GetEnumerator())
            using (var right = y.GetEnumerator())
            {
                while (true)
                {
                    bool leftHasAnother = left.MoveNext();
                    bool rightHasAnother = right.MoveNext();
                    if (leftHasAnother == false && rightHasAnother == false)
                    {
                        return 0;
                    }
                    var branchComparison = leftHasAnother.CompareTo(rightHasAnother);
                    if (branchComparison != 0)
                    {
                        return branchComparison;
                    }
                    var nextComparison = comparer.Compare(left.Current, right.Current);
                    if (nextComparison != 0)
                    {
                        return nextComparison;
                    }
                }
            }
        }
    }
}
